1. Field of the Invention
The present invention relates to a switch device that performs switching on and off of electric signals by bringing contact points into contact with each other and separating the contact points from each other.
2. Description of the Related Art
A microrelay that is a switch device is manufactured by semiconductor fine processing technology, and switches various electric signals such as radio-frequency signals. Such a microrelay has a number of advantageous features such as size that is smaller than a conventional relay, and therefore, has attracted public attention in recent years. Examples of such microrelays are disclosed in Japanese Unexamined Patent Publication Nos. 2001-291463, 2000-164104, 11-111146, and 2-100224, and Japanese Utility Model Gazette No. 2532487.
FIG. 1 is a side view of a first conventional microrelay. In the microrelay illustrated in FIG. 1, a movable spring 510 is disposed above a substrate 520. The movable spring 510 has one end fixed by a fixing member 530, and the other end as a free end. A contact point 512 that serves as a movable contact point is provided at the free end. Another contact point 522 that serves as a fixed contact point is provided on the substrate 520, and is located to face the contact point 512.
When a voltage is applied between the contact point 512 and the contact point 522, the contact point 512 moves toward the contact point 522 in synchronization with the movement of the movable spring 510 by virtue of electrostatic attraction, as shown in FIG. 2. The contact point 512 finally comes into contact with the contact point 522. Thus, the microrelay is put into an ON state.
FIG. 3 is a side view of a second conventional microrelay. In the microrelay illustrated in FIG. 3, a movable spring 510 is disposed above a substrate 520. The movable spring 510 has both ends fixed by fixing members 530. A contact point 512 that serves as a movable contact point is provided in the approximate center of the surface of the movable spring 510. On the substrate 520, another contact point 522 that serves as a fixed contact point is provided to face the contact point 512.
When a voltage is applied between the contact point 512 and the contact point 522, the contact point 512 moves toward the contact point 522 in synchronization with the movement of the movable spring 510 by virtue of electrostatic attraction, as shown in FIG. 4. The contact point 512 finally comes into contact with the contact point 522. Thus, the microrelay is put into an ON state.
In the above described first conventional microrelay, however, the entire surface of the contact point 512 cannot be brought into contact with the entire surface of the contact point 522. Because of this, it is difficult to stabilize the value of contact resistance, and only particular spots in the contact points are abraded. As a result, the service lives of the contact points become short.
In the second conventional microrelay, the surface of the contact point 512 can be brought into contact with the surface of the contact point 522, as shown in FIG. 4. However, the second conventional microrelay has more drawbacks than the first microrelay, in terms of the flexibility of the movable spring 510.
More specifically, the flexibility σ of the movable contact point is expressed as σ=PL3/3EI (Equation 1), where L represents the length of the movable spring 510, E represents the Young's modulus, I represents the second moment of area, and P represents the load applied to the movable contact point in the first conventional microrelay. On the other hand, when the load P is applied to the movable contact point in the first conventional microrelay, the flexibility σ of the movable contact point is expressed as σ=PL3/192EI (Equation 2).
The distance (the contact point distance) between the movable contact point and the fixed contact point in an OFF state is determined by the required withstand voltage between the contact points, the isolation characteristics, and the likes. In a case where the force for driving the movable spring 510 (i.e., the load P in Equations 1 and 2) is constant, so as to obtain the same contact point distances in the first and second conventional microrelays, the movable spring 510 of the second conventional microrelay needs to be four times as long as the movable spring 510 of the first conventional microrelay. Therefore, the second conventional microrelay cannot be made smaller in size.
In a case where the length of the movable spring 510 is constant, so as to obtain the same contact point distances in the first and second conventional microrelays, the second conventional microrelay requires a driving force 64 times as great as the driving force required in the first conventional microrelay. Since the electrostatic attraction between the contact point 512 and the contact point 522 is proportional to the square of the voltage to be applied between the contact point 512 and the contact point 522, the voltage to be applied between the contact point 512 and the contact point 522 in the second conventional microrelay needs to be eight times as high as the voltage to be applied between the contact point 512 and the contact point 522 in the first conventional microrelay. Therefore, there has been an increasing demand for a method of reducing a required driving voltage and stabilizing the contact resistance, without an increase in size.